Over the last 30 years there have been increasing proportions of internal combustion engines that are equipped with electronic fuel injection (EFI). The reason for this is multifold: increased reliability, performance, and longevity are key factors, along with significantly tighter engine calibration over the full engine operating range. As of the end of the 1990's, practically all original equipment manufacturer (OEM) passenger car engines were converted from carburetion to EFI; smaller engines like motorcycles followed suit.
The automotive aftermarket also followed the trend, offering EFI conversion systems for existing engine applications. Many of these EFI conversion systems were offered to retrofit existing carburetor-equipped engines, with the carburetor eliminated and replaced with a throttle body for air flow regulation. Other systems provided by the aftermarket serve as a replacement to OEM engine controls, permitting adjustments to calibrations and operating parameters.
Engine controls for automotive aftermarket engines most often employ fuel injection methods involving port or centralized throttle fuel metering strategies. These systems use one or a plurality of electromechanical solenoids to control the flow of a combustible hydrocarbon such as gasoline and inject the fuel into the airstream in order to produce a desired air-fuel ratio for combustion within the cylinder. These fuel injector solenoids are most often located in the individual port runners upstream of the air intake valves, or right above or below the air throttle plates.
An automotive engine has a large dynamic operating range and the air-fuel operating range requirements can be extreme, especially for a high-output or air boosted engine. This dynamic operating range is often expanded compared to an OEM application, which places additional demands on the controls. In particular, the operating range of fuel injectors for aftermarket use can place the fuel injectors outside of their intended use. Fuel injectors are sized such that they provide the required fuel mass at the highest engine mass air flow rates. High crankshaft revolutions-per-minute (RPMs) and high mass air flow rates require larger injector flow rates. However, these same injectors are needed to accurately operate the engine during idle and low engine output regions. This low operating range translates into very small time duration pulse widths for operating the fuel injectors.
Solenoid fuel injectors utilize an electromechanically-operated pintle valve which is magnetically coupled to an electric solenoid. A current flow in the solenoid produces a magnetic field, and this magnetic field causes the pintle valve to move within the bore of the fuel injector. The pintle valve movement opens a metered orifice arrangement which permits the flow of fuel. The valve as designed is intended to operate in a flow/no-flow arrangement, and the duration of the applied solenoid current dictates the amount of mass fuel flow.
Due to the fact that the current within a solenoid coil ramps up after its initial application due to the inductance of the actuator solenoid coil, there is an inherent lag time between the application of solenoid current and the build-up of the magnetic field around the coil. This in turn causes a delay in time between the first application of current and the movement of the pintle valve. Determination of this time delay is important for the prediction of the mass of fuel flow through the injector for a given solenoid current application time.
The ramp-up time of the solenoid current is dependent on the inductance of the coil, the coil resistance, and the applied voltage. In a practical vehicle engine application, the voltage available to the fuel injector solenoid is not always constant. Situations such as cold starting, vehicle charging variability, electrical load variations such as headlights, heater blowers, etc., affect the instantaneous voltage available to the solenoid. This change in voltage will change the dynamic rate of solenoid energizing and hence, the time delay in pintle valve movement. The effect of this voltage variation is significant over the realistic range of available battery voltages within a vehicle.
It is therefore important to determine the dynamic characteristics of the fuel injector opening time as a function of battery voltage. However, information regarding these dynamic characteristics is not readily available.